For enclosed switchboards such as motor control centers, in general, a box-like panel frame is divided by shelves into a plural number of compartments, each compartment accommodating a pullout control unit. The control unit is of such a circuit configuration that various pieces of control equipment including a circuit breaker, an electromagnetic switch, and a control relay are placed on a common frame to provide a desired control function. The main circuit, or occasionally the control circuit thereof is so constructed as to automatically connect to and disconnect from the corresponding circuit on the panel frame side by a put-in and pull-out operation.
Contacts are so arranged on the rear of the control unit that putting in the control unit brings a power contact into connection with a bus bar (generally a vertical bus bar) arranged on the panel frame of the switchboard, through which power is supplied to each on-board piece of equipment. This also brings a load contact into connection with the load side terminal, thereby supplying the load side with power switched on and off by way of the control unit.
The enclosed switchboard provided with such a drawer type control unit is so designed that the front door of the panel frame can be closed only with the units in their retracted positions. Meanwhile, in the test and disconnected positions with the contacts drawn out of the bus bars the control units are projected from the front of the panel frame, preventing closing of the door.
In the conventional switchboard described above the door can not be closed in the disconnected and test positions but only in the connected position, necessitating that the door be left open while checking the interior, in the testing position or the disconnected position. However, leaving the door open impairs the enclosed function of the switchboard, allowing for electric shock and other dangers due to the emission of arcs and substances out of the switchboard in case of accidents. It may also block the passage and hamper operators from going through, sometimes causing injuries or damage due to accidental bumping.
For these reasons, when any control unit need not be placed in the connected position for a long time, it is removed and kept separately so as to allow the door of the switchboard to be closed to maintain its enclosed function and keep the passage open.
Taking into account the above background, the purpose of the present invention is to provide an enclosed switchboard in which the door can be closed in the disconnected and test positions of the control units thereof as well as in its connected position.